The Section has established a Laboratory of Muscle Enzyme Histochemistry that processes up to 300 muscle and nerve biopsies per year for diagnostic studies. Examined muscle specimens are from patients with neuromuscular manifestations related to various systemic autoimmune, viral, metabolic or endocrine diseases, patients with HIV infection, and patients with primary neuromuscular diseases, such as polymyositis, dermatomyositis, neurogenic muscular atrophies, muscular dystrophies, post-polio syndrome, polyneuropathies, mitochondrial encephalomyopathies and biochemical/genetic muscle disorders. The laboratory is also involved in various immunological, biochemical and virological studies that examine the susceptibility of the muscle and nerve to immune or viral mediated injuries. These include: (a) Study of the mechanism of muscle regeneration by examining changes in the antigenic properties of satellite cells and the role of adhesion molecules N-CAM, I-CAM, polio receptor, MAG and Po in muscle-nerve interaction; (b) study the susceptibility of muscle and nerve to infection with retroviruses and the ability of HIV or HIV-infected lymphoid cells to infect human myotubes in culture and induce expression of MHC-antigens; (c) study the expression of polio virus receptor in human muscle and the ability of the polio virus to infect and replicate in human myotubes. The infection of the muscle with other enteroviruses implicated in the pathogenesis of inflammatory myopathies is also examined; (d) study the toxicity of AZT to muscle mitochondria by applying various concentrations of AZT to human muscle in culture; (e) use of animal models to study the immunopathogenesis of neuromuscular diseases, which include: (i) examination of muscles from monkeys infected with simian immunodeficiency virus to study the mechanism of the retrovirus-induced inflammatory myopathy; (ii) study of the muscle, heart, and brain mitochondria from rats injected with AZT to assess structural, metabolic and functional changes in their mitochondria; (iii) study of the muscle and fascia from rats fed with contaminated L-tryptophan to establish a model for eosinophilia myalgia syndrome; and (iv) study the changes induced in rat sciatic nerves after intraneural injection with immunoglobulins from patients with autoimmune demyelinating polyneuropathies to examine the presence of circulating myelinotoxic, neuronotoxic or axonotoxic autoantibodies.